Daylight harvesting is an energy saving solution for smart lighting systems which maintains a desired light intensity level in a room constant by dimming the artificial light as a function of the amount of daylight that enters the room from the windows. An efficient solution to deliver on this goal is the use of light sensors, which enable a feedback loop control of the lighting output of dimmable luminaries. However, this solution does not take into account other features of the lighting ambience, such as those concerning the spectral composition of the light, e.g. color temperature.
Color temperature is widely acknowledged as an important feature of the lighting scene as it is known to have effects on perception and on non-visual effects of lighting. As a matter of fact, variable color lighting is increasingly being used in applications where the ambience is crucial, such as museums, exhibitions etc., in working environments, such as offices, schools etc. to enhance performances (the so called “task related lighting”), as well as in any other application were the user experience can benefit from different ambiences. The effectiveness of the lighting system in controlling the ambient chromaticity is effected by the contribution of daylight to the overall lighting of the room.
In WO 2009/044330 a variable color lighting system is disclosed. The variable color lighting system comprises a light source, a controller for controlling the light source, and a light sensor. The light sensor is arranged for sensing spectral information comprising at least two different portions of a spectrum of light impinging on the light sensor. The controller is configured for receiving a sense signal and for generating a drive signal supplied to the light source to determine the spectrum of the light emitted by the light source in dependence on the spectral information from the light sensor. The effect of the measures is that the sensing of the spectral information of the light impinging on the light sensor enables the controller to adapt the color temperature of the light emitted by the light source such that the perceived color temperature more closely corresponds to an intended color temperature. However, by adapting the color temperature of the light emitted by the light source such that the perceived color temperature more closely corresponds to an intended color temperature according to the method described in WO 2009/044330 the light intensity of the light in the room may be unintendinly altered.